This invention relates to digital communications, and in particular to channelized digital data communications over digital loop carrier wired networks. The invention has particular application in distributed digital switching systems for high-speed digital communications.
Asynchronous Transfer Mode (ATM) based communication is a high-speed packet-based switched communication technique wherein xe2x80x9ccellsxe2x80x9d (packets) are communicated between a source node and a target node through one or more switches. ATM benefits from high-bandwidth transport media. T1 time division multiplexed (TDM) transmission formats are widely deployed in North America and correspondingly E1 is used in Europe for the transport of multiplexed voice channels and other digital communication. A T1 signal consists of 24 DS-0 channels transported with an eight-bit sample every frame period, with the frame repeating each 125 xcexcs to yield an overall bit rate per DS-0 channel of 64,000 b/s. Higher bandwidth formats are known and used but are much more expensive and less available. DS-3 channels have a reported rate capacity of about 45 Mb/s.
It is desirable to have a single ATM stream with a bandwidth in excess of the T1 transmission format (1.544 Mb/s) but less than is available over the much more expensive DS-3 channel transmission format (45 Mb/s).
ATM cells can be communicated over T1 transport media by dividing up the ATM stream and using inverse multiplexing techniques. In order to do so it is necessary to reconstruct the cell order. The ATM Forum has adopted an IMA standard for inverse multiplexing of ATM which relies on a stream of control signalling cells and more specifically the existing T1 UNI standard to support IMA. An intricate payload block mapping technique is used to reconstruct cell order. This results in considerable cell overhead and is difficult and expensive to implement.
Those of ordinary skill in the art should be aware of the background information found in the following typical publications:
xe2x80x9cSynchronous Optical Network (SONET) Transport Domains: Common Generic Criteria,xe2x80x9d Bellcore GR-253-CORE, Issue 2, December 1995.
xe2x80x9cFunctional Architecture of Transport Networks Based on ATM,xe2x80x9d ITU-T Recommendation I. 326, draft revision June, 1997.
xe2x80x9cVoice and Telephony over ATM to the Desktop Specification,xe2x80x9d ATM Forum, AF-VTOA-0083.000, May 1997.
xe2x80x9cInverse Multiplexing for ATM (IMA) Specification,xe2x80x9d ATM Forum, AF-PHY-0086.000, April 1997.
What is needed is a mechanism to optimize usage of available resources, such as T1 resources, and to support ATM data streams with greater flexibility.
According to the invention, in a digital multi-path communication system employing asynchronous communication, a single byte prepended to each cell or unit of telecommunication information is used as a key for reconstructing information as required for maintaining data order and integrity. Specifically, a single ATM traffic stream is carried over a plurality of lower bandwidth media and interfaces between an original source and an ultimate destination, such as via multiple T-1 or E-1 interfaces, using inverse multiplexing assisted by a prepended byte at the beginning of each ATM cell, the prepended byte being simply a count used as the key for recovering proper order of the ATM cells.
The invention will be better understood by reference to the following detailed description in connection with the accompanying drawings.